Participants
This population-based cross-sectional study consisted of a home questionnaire and a field survey conducted by the Department of Stomatology, People’s Hospital of Xiangyun affiliated with Dali University between September 2020 and January 2021. We calculated the minimum sample size using Epi Info 7 with a 95% confidence level, a 0.05 margin of error, a design effect of 2, a 69.5% reported prevalence of OMLs [8], and a 10% additional sample size to compensate for the possible sample loss. Finally, we obtained a minimum sample size of 724. We recruited approximately 4000 participants from four primary schools and six preschools located in four geographical regions (eastern, southern, western, and northern) in Xiangcheng Town, Xiangyun County in Yunnan Province through the 2020 National Oral Health Comprehensive Intervention Program for Children in China. The government of Yunnan Province announced that Xiangyun County had eliminated poverty in September 2018 [9]. The per capita disposable income of Xiangyun County in 2019 was 37,689 Yuan (4997 Euro) [10], equivalent to ~ 6000-Yuan per month per household from two full-time incomes. This study was approved by the Ethics Committee of the People’s Hospital of Xiangyun (No. 2020069). Informed consent was obtained from the guardians of all participants.
Exposures
The home questionnaire (Additional file 1) was administered to the guardians, and consent was obtained at that time. Variables collected through the questionnaire consisted of participants’ basic information (sex, age group, and ethnicity), chronic disease history, and SES, which included whether children had siblings, caregivers, parental education, last-month household income, and residence status. The variables were considered as exposures to explore whether they were associated with OMLs morbidity.
Outcomes
To define the OMLs, we applied the World Health Organization guidelines [11, 12] and referred to the textbook Oral and Maxillofacial Pathology [13]. Here, however, oral ulcer referred to any ulcer lesion in mouth due to a wide range of etiologies, including trauma, infection or inflammation.
In the presurvey preparation, a specialist provided a training program for five examiners by presenting 50 color images. These images covered the full spectrum of oral mucosal alterations and lesions expected during the survey. Following the training, the examiners continued learning until they obtained full marks during the testing session on the same images. Before starting a new-day survey, the examiners repeated the learning and testing processes. To achieve consistency, the inter-examiner Kappa value was calculated. Examinations assessing inter-agreement [14] took place in each examiner’s first five participants. The results were compared between examiners 1 and 2, 2 and 3, 3 and 4, 4 and 5, and 5 and 1. The Kappa scores were between 0.81 and 0.85, which met the agreement criteria.
During the survey, diagnoses were confirmed by a specialist when examiners were unsure of the findings. In the field survey, oral examinations were performed under artificial and natural light, with the children in a standing position. The examiners inspected and palpated using a mirror, explorer, cotton swab, and sterile gauze in the sitting position. The examination sequence was as follows: face, lip, buccal cavity, tongue, mouth floor, hard palate, soft palate, gum, and alveolar ridge. We adhered to the local hospital’s guidelines on infection control. At the end of our survey, we wrote down our suggestion of our findings on conclusion letters to guardians. The letters also stated the time and the place of our oral medicine service. Some children were treated by us, although some did not visit us.
Statistical analysis
Categorical variables were expressed as numbers and percentages (%). Statistical significance was set at p < 0.05. We replaced missing data on caregivers (n = 132, 4.2%), parental education (n = 81, 2.6%), and las-month household income (n = 134, 4.3%) with the mode of each variable when doing unadjusted or adjusted regression to analyze the risk factors (sex, age, caregiver, parental education, and last-month household income) associated with the presence of OMLs among the children. All statistical analyses were performed using SPSS 26.0.